Silver halide color photographic materials typically have a multi-layer constitutional light-sensitive film, coated on a support, comprising three kinds of silver halide emulsion layers selectively sensitized so that the layers have light-sensitivity usually to blue-light, green-light, and red-light respectively.
For the formation of color photographic images, photographic couplers for the three colors of yellow, magenta, and cyan are incorporated in the light-sensitive layers. The photographic materials, after having been exposed to light, are subjected to color development with a so-called color developer. The coupling reaction between the oxidation product of an aromatic primary amine and the coupler results in the formation of colored dyes. The coupling reaction rate is preferably as high as possible, and the couplers are preferred to have a high colorability so as to obtain a higher color density within the limited development time.
In addition, the yellow, magenta, and cyan couplers are required to be fixed individually to the respective silver halide emulsion layers each having a selective sensitivity to blue, green, or red light, respectively, to prevent color stain. Therefore, the couplers to be used in practice are to have a long-chain aliphatic group in the molecule as a diffusion-resistant group.
In practical use of such couplers having a hydrophobic diffusion resistant group, it is known to dissolve these substances in a high boiling solvent (oil-former) and a low boiling or partially water soluble auxiliary solvent and then to disperse this solution in an aqueous medium usually containing a hydrophillic binder, such as gelatin, and surfactant. After removal of the low boiling auxiliary solvent the hydrophobic substance is present in the aqueous medium in the form of small particles or droplets of oil-former containing the hydrophobic substance. The process was first described in U.S. Pat. No. 2,322,027.
This method of dispersing hydrophobic substances has persisted substantially in this form to the present day, although various other types of substances have been proposed for use as oil-formers. Examples of useful oil-formers or coupler solvents are described by, for instance, Jelley et al U.S. Pat. No. 2,322,027, Sawdey et al U.S. Pat. No. 2,533,514, Fierke et al U.S. Pat. No. 2,801,171, Smith U.S. Pat. No. 3,748,141 and Krishnamurthy U.S. Pat. Nos. 4,540,657 and 4,684,606.
It is desirable that the color photographic materials described heretofore deliver consistent color images throughout the processing of large volumes of these materials through the various processing solutions. Hence, it is required that the color photographic materials have a low sensitivity to variations in the composition and pH of these solutions which inevitably occur in the trade due to the processing of large quantities of material. Since the color images are formed in the color developer solution, the variability of its composition and pH are most important with regard to delivering high quality color images consistently.
The selection of color dye-forming coupler used can have a marked effect on the color reproducibility of the light-sensitive material. Methods of improving color reproducibility by use of megenta couplers which form dyes having little or no secondary absorptions are disclosed in the art including U.S. Pat. No. 3,725,067 and Japanese Patent Open to Public Inspection Nos. 42045/1983, 171956/1984, 43659/1985 and 190779/1985. The pyrazoloazole magenta couplers significantly improve color reproducibility. However, a major problem with these couplers is that the density of the dye image formed exhibits high variability when processing conditions change, in particular the pH of the color developer. This problem has been described in European Patent Application No. 0422595A1 which teaches the use of compounds having a hydroxyl group and an ester group used in combination with pyrazoloazole magenta couplers.
In the present invention, it has been found that this sensitivity to developer pH can be greatly reduced by the use of pyrazoloazole magenta couplers in combination with a long chain unsaturated alcohol. It has also been found that this combination produced unexpected increases in coupling reactivity.